This invention relates to a photosensitive composition which is useful for a fine working in the manufacture of for example a semiconductor element, a TFT (thin film transistor), a photo-disk, etc and method of forming a pattern using the photosensitive composition. Further, this invention relates to a transparent resin useful for optical material or coating material.
In the manufacture of electronic parts such as an LSI, a fine working technique utilizing a photolithography has been employed. In this fine working technique, a resist film is first formed by coating a resist solution onto a semiconductor substrate for instance. The resist film thus formed is then exposed to light through a prescribed mask pattern, and subsequently subjected to various treatments including an alkali-development, thereby forming a resist pattern. This resist pattern is then utilized as an etching resistant mask in a dry etching process, and the exposed portions of the substrate are etched away to form a pattern of fine line or window thereby obtaining a desired pattern. Finally, the resist pattern remaining on the substrate is removed through ashing.
Therefore, the resist to be employed in this process is generally required to have a high dry-etching resistance. In view of this requirement, a resist comprising an aromatic compound has been extensively employed. For example, many kinds of resists comprising an alkali-soluble novolak resin as a base resin have been developed up to date.
In view of a trend in recent years to further increase the integration of semiconductor elements such as seen in an LSI, the aforementioned fine working technique in recent years has been advanced to such a degree that makes it possible to realize a fine pattern of the order of sub-half micron. It is expected that this trend to increase the integration of semiconductor elements becomes more prominent in future. In order to meet such a trend, the use of light source of shorter wavelength in photolithography is now being studied. For example, a method for forming a finer resist pattern through the use of ArF excimer laser (193 nm in wavelength) or the quintuple harmonic of YAG laser (218 nm in wavelength) has been tried at present.
However, the aforementioned conventional resist comprising a novolak resin as a base resin which has been generally employed up to date is generally characterized by its prominent absorption of the light of short wavelength at the benzene nucleus of the novolak resin. Therefore, it is impossible, because of this prominent light absorption, to allow the exposure light to reach deep enough to an interface between the resist film and the substrate. As a result, it has been very difficult to form a fine pattern of excellent shape while assuring high sensitivity and high precision.
As mentioned above, since the resist comprising a novolak resin as a base resin is insufficient in transparency to the light of short wavelength in spite of its excellent dry-etching resistance and alkali-developing properties, it is now strongly demanded to develop a new resist which is suited for use in a photolithography where the ArF excimer laser (193 nm) or the quintuple harmonics of YAG laser (218 nm) can be employed.
In view of this, a resist where an alicyclic compound is employed in place of an aromatic compound is recently attracting many attentions. For example, as one example of a resist which is excellent in dry etching resistance and in transparency to a light of short wavelength, a resist comprising a polymer having an adamantine skeleton as a base resin thereof is proposed in Japanese Patent Unexamined Publication H/4-39665. This patent publication also discloses an example where a compound having an adamantine skeleton is copolymerized with an acrylic compound having a carboxylic group to provide a copolymer having an alkali-solubility, which is then subjected to an alkaline development to form a resist pattern.
However, there are various problems that will be encountered in a process of forming a resist pattern through an alkaline development of a resist comprising an alicyclic compound, because the alkali-solubility of an alicyclic structure such as the adamantine skeleton differs greatly from that of carboxylic group. For example, the solubility and removal of a given region of a resist film may become non-uniform at the occasion of development, thereby inviting not only the deterioration of resolution, but also a partial dissolution even in a region of the resist film which is originally intended to be kept unremoved, whereby causing a generation of cracks or surface roughening in that region of a resist film. Moreover, an alkali solution may penetrate into an interface between the resist film and the substrate, thereby causing a peeling of the resist pattern. Additionally, a phase separation between the alicyclic structure portion and the carboxylic group portion of the polymer may more likely take place, thus making it difficult to prepare a homogeneous resist solution and to obtain a resist solution having a satisfactory coating property.
Moreover, due to a high polymerizability which is peculiar to an alkaline resist, the aforementioned polymer is prone to be further polymerized. When the molecular weight of this polymer is increased excessively, the alkali-solubility thereof would be greatly deteriorated, thus making it difficult to obtain an alkali-soluble resin exhibiting a sufficient solubility for use as a resist. On the other hand, if the molecular weight of the polymer is decreased so as to improve the solubility thereof, not only the transparency of the resist, but also the adhesivity of pattern after the development thereof would be deteriorated. Moreover, the dry-etching resistance of a pattern of the polymer when the pattern is subjected to any of various dry etching processes is inferior as compared with a resist comprising an aromatic compound.